1. Field of the Invention
The invention relates to a data projection device used in cameras that projects a data pattern generated on a liquid crystal cell onto photographic film, and more particularly to a mechanism for maintaining the definition of the data image to be projected in this type of data projection device.
2. Description of the Related Art
FIG. 7 shows the general structure of a data projection device for projecting data such as a date onto photographic film inside a camera. As shown in this figure, data projection device for cameras 100 is installed in the space between backlid 101 of the camera main unit and platen 102 positioned roughly in parallel to said backlid 101 inside the camera main unit. The surface of platen 102 opposite from backlid 101 is the film installation area along which photographic film 103 is to be installed. Data such as a photographing date can be projected onto this photographic film 103 through opening 102a provided in platen 102.
Data projection device for cameras 100 has a structure in which circuit board 114 on which IC chip 113 is mounted, monitoring liquid crystal display device 115, and data projection liquid crystal display 116 are all sandwiched between first frame plate 111 and second frame plate 112. The two frame plates 111 and 112 are fastened to each other by putting multiple dowels 112a formed on the second frame plate side through through-holes 111a formed on the first frame plate side and flattening their tops.
Monitoring liquid crystal display device 115 for displaying various types of data for the operator is installed and fastened to the inside of second frame plate 112, cover glass 121 is installed on the surface of said display device 115 to protect it, and the surface of the cover glass 121 is exposed to the outside through opening 101a provided in camera backlid 101. Data projection liquid crystal display device 116 located in the position corresponding to opening 102a provided in back plate 102, is installed on the inside of first frame plate 111.
IC chip 113 mounted on circuit board 114 is covered and protected by molding material 122. Drive signals are supplied from the circuit board 114 to monitoring liquid crystal display device 115 via flexible connector plate 123. This connector plate 123 functions as the support plate for pressing display device 115 from the back side toward second frame plate 112 and securing it therein.
Spacer plate 124 prevents connector plate 123 from falling, and this plate 124 also prevents display device 116 from tilting.
Likewise, data projection liquid crystal display device 116 located on the opposite side is electrically connected to circuit board 114 by a pair of connector plates 125 and 126, and is pressed toward first frame plate 111 by these connector plates. Note that data projection device 100 having this configuration is fastened inside the camera main unit by fastening plate 127.
FIG. 8(A) schematically shows a data-projection optical system equipped with data projection liquid crystal display device 116. Various components comprising this optical system are also integrated into data projection device 100. Data projection liquid crystal display device 116 is equipped with liquid crystal cell 201 in which liquid crystals are sealed between a pair of electrode substrates, and can form the data pattern to be projected into photographic film 103 as a translucent area. The light emitted by light source lamp 202 is guided to liquid crystal cell 201 via reflection mirror 203, and is then guided to photographic film 103 after excess light is eliminated by liquid crystal cell 201. As a result, a data image corresponding to the data pattern is projected onto photographic film 103.
Since liquid crystal cell 201 alone cannot sufficiently eliminate excess light, the data image projected onto photographic film 103 via the translucent area of liquid crystal cell 201 sometimes has unclear edges. In order to avoid this problem, a conventional method eliminates excess light by placing light-shielding mask 206 between light source lamp 202 and liquid crystal cell 201.
As shown in FIG. 8(B), light-shielding mask 206 provided for this purpose is provided with translucent area 208 defined by multiple translucent segments 208a having shapes that correspond to the individual segments 207 on the side of liquid crystal cells 201 for forming data patterns, and with light-shielding area 209 formed in the rest of the area. Therefore, by providing this light-shielding mask 206, excess light is eliminated from the light that enters liquid crystal cell 201.
Note that, for light-shielding mask 206, a metal film is usually formed on a glass substrate according to the specified pattern using a film-formation method, such as plating and vapor deposition, and the area without the metal film is used as translucent area 208.
Because the data projection device for cameras having the aforementioned configuration is equipped with light-shielding mask 206, excess light can be eliminated from the light that enters liquid crystal cell 201. However, light is also diffused when passing through liquid crystal cell 201. Consequently, data image definition deterioration due to this kind of diffusion still remains.
To avoid this problem, one possibility is to locate light-shielding mask 206 on the outgoing-light side of liquid crystal cell 201. This can prevent data image definition deterioration that will be caused by the diffusion of the light passing through the liquid crystal cell.
Note that glass substrates are usually used for the pair of electrode substrates which comprise liquid crystal cell 201. If thick substrates can be used for these glass substrates, their processability during manufacturing will improve, resulting in higher yields which is desirable. However, since the light-shielding mask is located on the outgoing-light side of the liquid crystal cell, light is still diffused after passing the translucent area formed by the liquid crystals sealed between the pair of electrode substrates and before reaching the light-shielding mask by passing through the glass substrate on the outgoing-light side.
As explained above, merely increasing the thickness of the glass substrates to improve yield also increases the amount of light diffused when passing through said glass substrates, in proportion to the thickness increase. As a result, the definition of the data image to be projected onto the photographic film deteriorates, which is undesirable.